Magnetic heads are employed to operate hard disk drives. A magnetic head can include a reading head and a recording (i.e., writing) head. General structures and method of manufacture for prior art magnetic heads are disclosed, for example, in U.S. Patent Application Publication Nos. 2004/0097173 A1; 2007/0230063 A1; 2011/0294398 A1; and 2015/0260757 A1 and U.S. Pat. Nos. 8,291,743 B1; 8,361,541 B1; 8,443,510 B1; 8,717,709 B1; 8,735,565 B2; 8,964,333 B1; 9,153,261 B1; 9,321,146 B2; and 9,390,733 B2 the entire contents of which are incorporated herein.
Generally speaking, use of a rear bias material for a reading head requires use of a thin backside insulating layer. Incorporation of the material of the thin backside insulating layer and the rear bias material in electronic lapping guide (ELG) structure can result in electrical shorts through the thin backside insulating layer, and consequent error in estimation of true stripe height in sensor devices.
For example, in the case of a reading head employing dual free layers, a hard magnetic material such as a cobalt-platinum alloy is employed to fill a volume behind a read sensor and to form a rear bias material portion. The rear bias material portion provides a magnetic bias field to the read sensor. However, deposition of this hard magnetic material behind the backside edge of electronic lapping guides (ELG's) can cause a short with the ELG, which can misguide the lapping process that provides the target stripe height for the read sensors.